Engine starter gearing



May 10, 1949. .1. E. BUXTON ETAL 2,469,792

ENGINE STARTER GEARING Filed May 27, 1947 INVENTORS James 6.

Patented May 10, 1949 ENGINE ISTARTERGEARING ilames E; Buxton; Frank T;Gl'ifistian, and Rene E. DemurmilElmira; N. Ys assignorsto' BendixAviation iflonponatiomra corporation of Delaware Application May 27,1947;"Srial No; 7501726 :3 Claims. (01; 34-47) 1 The present inventionrelates toengine starter gearing and more particularly to a star terdrive of the type in 'wh'ich ap'inion is automatically traversed intoand out of mesh with a' 'ear of an'engine tobe started.

Engine starter drives as now commercially manufactured are generally oi-the socalled barrel type in which a smooth-bored-dr ive pinion isslidably journalled on the motor shaft ior 'longitudinal movementintoand out of mesh with-an engine gear, and is 'actu-atedbya controlnut threaded-on a *motor driven-screw :shaitfithespinion "being Iconnected to the control nut by a. hollow barrel member.

In order to secure reliable traversingaction-of thenut 'under allconditions or congealed lubricant -etc., it is necessary that theinertia of the nut, barrel and pinion as respects rotation be largerelatively to the inertia of these parts in respect to "longitudinalmovement. "This result may readily-be secured by increasing the-diameterof thebarrel while-preferably reducing "its "wall thickness, but whenthis practice is iollowed too far; undesired re'enga'gements of thepinion with the *eng'ine'gear after demes'hare encoun- 9 tered. Theseundesired reeng'agements are caused by the iact that the operatordoesznot ordinarily'open the starting switch at the instant the enginefires and demeshes the'pinion. The

starting motor therefore accelerates due *to' 'the release of thecranking load thereon and consequenltly traverses the control -nut,barreland=pinion back toward the-engine fly wheel "until the pinionstrikes the side of the rapidly rotating engine gear;causingunnecessarywear and noise.

It is an object of the present invention to provide a novel enginestarter drive having adequate rotational inertia to secure traversalunder adverse circumstances, but having means for preventingtraversal ofthe :pinion ba'c'k towardthe Eig; 2 is -a-section taken substantiallyentire -Riel- 3 is a detail in perspective, partly-broken away and 'in'section, of the barrel and pinion assembly; and

"Fig. 4 is a view similar to Fig. 2 0f a modified .iorm of theinvention.

Filn Fig. -1 oi the drawing, there is illustrated "answer sha'it i whiohmaybe the extended-"arma- *ture s'haiftoi astarting motor notillustratedthe outer end -oi which is .supported invan outboard bearing 2preferably attached to the iramemiithe startingmotor. A pinion 371ss'lidably iournalled on the power shaft for longitudinal "movement "intoand out or mesh "with a gear 4 of the engine to be started. I Lat-hollowsleeve i5 is fixed on the power shaft l asbymeans-lof a qiin6and'is*yield ably "c'onnect'ed by means oi -adrive :spring" '1 to ascrew-shafts which is :slidably tjournallied: :on a reduced portion 9 ofsaidsleeve, the screw shaft being retained on the sleeve by a stop Ii.

A .control nut "l 2 is threaded .on the screw shaft band is rigidlyconnected as indicated at: .i 3 to a=cyllndrical-barrel M which isrigidly attached to themiiiion-fi asrsh'own at 1:5. I

T-he threads of the-screw shaft :8 terminate ad jacen t-the idleposition of the controlnut -l2-1eaving a smooth portion I6 on'whichthecontrol nut is "free to rotate when the pinion zandbarrel asseniblyioverrun the screwsshait, and alight-compr ession anti-drift .spring .1.1 bearing on the conitrolrnut tZ and stop nut :ltl: urges the stop nutto'wardidle' position. Means :for causing the eontro'l nut to enter uponthe threads :of the :screw shaft-so as to be traversed to thevi'ightiupon acceleration ioi' the 'screw shait :is provided in the formof a re-entry spring ?I 8 flocatedzin the inner end o'f the barrel M andbearingagainsta thimble E9 whichznormally crests against the stop nut11. Means for limiting the :expansion of the :reentry 'sp'ring l iiflislprovided in the form rof a lock zring 2 seated-Tina grooveiintheiinterior-oi the barrel in pos'it'ionto en'gage the leripheralilange- 22 of thelthimble. 119 5 0 as to maintain the re-entr-yspring under initial compression.

.:.-In:.order to increasethe rotational inertia of the pinion and barrelassembly, a hollow cylindrical inertia member 23 of considerably greaterdiameter than the barrel is rigidly mounted on the exterior thereof.This inertia member is also utilized to prevent undesired traversal ofthe pinion and barrel assembly toward the engine gear when the parts arerotating. This function is accomplished by mounting the inertia member55 eccentrically with respect to the barrel so that rotation thereofaround the axis of the barrel causes a radial thrust to be applied tothe control nut I2 thereby developing a frictional gripping effect ofthe control nut on the threads of the screw shaft.

As best shown in Figs. 2 and 3, the rigid attachment of inertia member23 to the barrel I4 is preferably brought about by forming depressionsor dimples 24 in the inertia member at substantially diametricalpositions in relation to the barrel and arranged to closely engage thebarrel, while the intermediate portion of the inertia member 23 is fixedto the barrel by welding or brazing as indicated at 25 so as to form arigid permanent connection.

In the operation of this drive, starting with the parts in the positionsillustrated in Fig. l, rotation of the power shaft l in the direction ofthe arrow is transmitted to the screw shaft 8,lcausing the control nut 2to be traversed to the right along the screw shaft until the pinion 3 isfully meshed with the engine gear 4, at which time the control nut l2engages the stop nut l I whereupon the pinion 3 is constrained to rotatewith the screw shaft to crank the engine. During this traversal, theinertia member 23 by virtue of its large diameter and comparatively thinwall, greatly increases the rotational inertia of the pinion and barrelassembly relative to its inertia as respects longitudinal movement so asto insure traversal of the pinion into mesh under the most adverseconditions.

When the engine fires, the acceleration of the engine gear 4 istransmitted to the pinion 3, causing the pinion and barrel assembly tooverrun the screw shaft 8 whereby the control nut 12 is threaded backalong the screw shaft until it runs off the ends of the threads thereon.Since the pinion 3 is thus demeshed from the engine gear 4, the pinionand barrel assembly quickly decelerates to the speed of the screw shaft,whereupon the re-entry spring it becomes effective to reengage thecontrol nut l2 with the ends of the threads on the screw shaft 8. Itwill be understood that this demeshing action normally takes place in afraction of a second so that the screw shaft and motor shaft are stillrotating substantially at cranking speed.

If, under these circumstances the operator fails to open the startingswitch so as to deenergize the starting motor, the power shaft l andscrew shaft 8 will be rapidly accelerated by the release of the crankingload therefrom, and this acceleration will tend to traverse the controlnut and the pinion and barrel assembly toward the engine gear. At thistime, however, the pinion and barrel assembly including the inertiamember 23 are in rotation, and the eccentricity of the inertia member 23causes it to press the control nut l2 against the threads of the screwshaft on the side to which the eccentric inertia member is attached. Theeccentricity of the inertia member is so related to the rotationalmoment of inertia of the pinion and barrel assembly and theaccelerational characteristics of the starting motor that adequatelateral pressure is brought to bear Fig. 4 illustrates a modification ofthe inven- I tion in which the eccentric weighting of the barrel memberis obtained by forming the eccentric cylindrical member integral withthe barrel itself. As there shown, the interior cylindrical surface 26of the barrel I4 is coaxial with the screw shaft 8 as in the firstembodiment of the invention, but the exterior cylindrical surface 21 ofthe barrel is abaxial thereto so as to weight the barrel eccentrically.

Rotation of the barrel will cause centrifugal force to apply radialpressure from the barrel to the nut to increase the friction of the nuton the screw shaft, and thereby oppose relative rotation therebetweenthe same as in the first embodiment of the invention.

Although but two embodiments of the invention have been shown anddescribed in detail, it will be understood that other embodiments arepossible and that changes may be made in the proportions and arrangementof the parts without departing from the spirit of the invention asdefined in the claims appended hereto.

What is claimed is:

1. In an engine starter drive, a power shaft, a pinion slidablyjournalled thereon for movement into and out of mesh with a gear of anengine to be started, a screw shaft, means connecting the screw shaft torotate with the motor shaft, a control nut threaded on the screw shaft,a barrel member connecting the control nut and pinion, a hollowcylindrical inertia member, and means for connecting the inertia memberto rotate with the barrel member while maintaining the inertia membereccentric thereto.

2. An engine starter drive as set forth in claim 1 in which said inertiamember is in the form of a cylinder having an internal diametersubstantially greater than the outside diameter of the barrel, andrigidly fixed thereto on one side.

3. An engine starter drive as set forth in claim 1 in which said inertiamember is in the form of a cylinder having an internal diametersubstantially greater than the outside diameter of the barrel, andrigidly fixed thereto on one side, said cylinder having inwardlyprotruding means for engaging the exterior of the barrel at pointscircumferentially spaced from its attachment thereto so as to preventlateral movement of the cylinder on the barrel.

JAMES E. BUXTON. FRANK T. CHRISTIAN. RENE E. DEMURE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,820,442 Cooper Aug. 25, 19312,117,999 Whitney May 17, 1938

